Les observations du vecteur champ magnétique dans la photosphère solaire révèlent de manière générale une valeur non-nulle de la divergence: on trouve un gradient vertical de l'ordre de 3 G/km pour la composante verticale du champ, non compensé par le gradient horizontal de la composante horizontale qui n'est, lui, que de 0.3 G/km (quelle que soit la résolution). Il faut alors rappeler que la quantité que l'on mesure par effet Zeeman est le champ magnétique H, qui est relié à l'induction magnétique B (à divergence nulle) par la relation B=µ0(H+M), où M est l'aimantation ("magnetization" en anglais). Dans les plasmas comme celui de la photosphère solaire, l'aimantation résulte du diamagnétisme de plasma qui est dû au mouvement de spirale des particules chargées autour du champ magnétique. La valeur usuellement admise pour la densité électronique, mais qui ne résulte que d'une détermination très indirecte, conduit à une valeur très faible de l'aimantation. Cependant, dans l'intérieur solaire, la vitesse thermique des électrons est beaucoup plus grande que leur vitesse d'échappement de la gravité de l'astre et même des protons, qui ne les retiennent pas complètement. Un modèle fait l'objet de l'article présenté. Les électrons s'échappent de l'intérieur dans un mouvement très lent, quasistatique, et s'accumulent dans les couches de surface. Ainsi, la densité électronique superficielle se trouve augmentée, et sa décroissance avec la hauteur permet d'expliquer la valeur observée de divH = -divM. Une telle structure est probablement à l'œuvre dans les étoiles de type solaire.

Poster

Plasma diagnostic measurements for linear to weakly non-linear plasma response: application to Mutual Impedance experiments and Relaxation Sounders

Bucciantini L.(1), Henri P.(1,2), Wattieaux G. (3),

(1)LPC2E, CNRS, Univ. Orléans, OSUC, CNES, Orléans +33 (0)2 38 25 51 26, [email protected]

(2)Lagrange, OCA, UCA, CNRS, Nice, +33 (0)4 92 00 39 74, [email protected]

(3)LAPLACE ,CNRS, Univ. Toulouse, Toulouse +33 (0)5 61 55 75 90, [email protected]

Keywords: Langmuir waves, non-linearity, mutual impedance probe, relaxation sounder, full-kinetic simulations, instrumental response prediction, plasma diagnostics.

ABSTRACT

Relaxation sounder experiments and mutual impedance experiments are popular plasma diagnostic techniques for the determination of characteristic plasma parameters: by actively perturbing the local plasma medium, they allow measurements of the in situ (absolute) plasma electron density, and in some cases the local magnetic field and electron temperature. Relaxation sounders and mutual impedance instruments have flown on several successful space missions, among which we recall the (still ongoing) Cluster II mission and the Rosetta mission, respectively. Both experiments consist of: (i) exciting the local plasma medium over a given frequency range, with a succession of sinusoidal signals at a fixed frequency and amplitude and (ii) measuring the electric field generated in the plasma at this same frequencies, from which an electric power spectrum is built. Such spectra typically exhibit resonances at the characteristic frequencies of the probed plasma (e.g. the plasma electron frequency, the upper hybrid frequency, the electron Bernstein modes), reflecting the plasma dielectric. However, active instruments for in situ plasma diagnostics emitting signals at energies comparable to the local electron energy are expected to trigger non-linear plasma responses, that might result in major perturbations of the medium, hence modifying locally the probed plasma dielectric.

In this context, this study aims at investigating the impact of high emission levels to the instrumental response of relaxation sounders and mutual impedance experiment that might introduce non-linear plasma responses. The investigation is performed by means of numerical simulations based on a full-kinetic 1D-1V electrostatic Vlasov-Poisson model. By investigating wave-wave and wave-particle non-linear effects triggered in the local plasma medium by active electric instruments, this study directly provides inputs for a better understanding of the instrumental response of relaxation sounders and mutual impedance measurements in space plasmas.

The rate at which the solar wind extracts angular momentum from the Sun has been predicted by theoretical models for many decades, and yet we lack a conclusive measurement from in-situ spacecraft. Here I present recent analysis (performed during my PhD under the supervision of Sean P. Matt at the University of Exeter) of the solar wind angular momentum flux from Parker Solar Probe, and I outline my current efforts in performing a multi-spacecraft analysis taking observations from both Parker Solar Probe and Solar Orbiter at different radial distances. In addition, I present some new and ongoing research that I am performing as a postdoc in the WHOLESUN ERC project (supervised by Sacha A. Brun at CEA Paris-Saclay). Here I wish to derive the energy input to the solar wind according to realistic RMHD simulations of the solar atmosphere. Please do not hesitate to contact me if you would like to discuss/collaborate on either topic I present here.

B. Gannouni¹, R. F. Pinto¹, A. Strugarek¹

¹ Département d’Astrophysique/AIM, CEA/IRFU, CNRS/INSU, Univ. Paris-Saclay & Univ. de Paris, 91191 Gif-sur-Yvette, France

Solar flares consist of episodes of intense EUV and X-ray emission that follow from quick releases of energy stored in coronal structrures with complex magnetic fields. Twisted magnetic flux-ropes are likely to play a central role in the triggering and evolution of solar flares, as they are susceptible to develop instabilities leading to quick energy releases in the form of strong coronal plasma heating and of particle acceleration. The interdependence between the large scale topology of the magnetic field and its small scale dynamics determines to a great extent the outcome of such processes. Detailed numerical simulations are thus required to determine the physical links between the magnetic field, the bulk plasma thermodynamics, the charged particle motions, and the corresponding observable electromagnetic signatures.

We will present recent simulations focusing on impulsive plasma heating and particle acceleration in modelled solar flares triggered in twisted coronal loops. We use a hybrid approach based on 3D MHD, test-particle and Particle-In-Cell (PIC) techniques.

We discuss the outcomes of the simulations in terms of the morphological and spectral properties of the forward-modelled emission in the context of the Solar Orbiter mission and of the STIX instrument.

Serge Koutchmy (1), Ehsan Tavabi (2), Jacques-Clair Noëns (3), Odile Wurmser (3), Jaime Vilinga (4) and Boris Filippov (5)
(1) IAP - CNRS and Sorbonne Univ. ; (2) Tabriz Univ. RI ; (3) OA Association PdM Obs. ; (4) Estado
Major-General das FAA, Luanda, Angola ; (5) Pushkov IZMIRAN , Russia

The prediction of the height of the forthcoming solar activity cycle (expressed by the Sunspot Number SN) is since 2019 the subject of many studies. They are mainly based on statistical and/or mathematical and/or Heuristic methods, taking parameters from the analysis of past cycles; they leaded to a ?predicted? cycle 25 similar to the preceding cycle 24, slightly lower, indeed. A few predictions try to use ?solar activity? parameters justified by the solid belief that the solar activity is fully governed by a dynamo mechanism occurring inside the Sun. The most popular dynamo model being the Babcock-Leighton (B-L) model describing the transformation of a general dipolar field of the rotating Sun into a toroïdal field through the differential rotation visualized near the surface. The regeneration of the dipolar field is another aspect of the model. Several puzzling features like the M- regions, the active longitudes, the occurrence of long- live big single sunspots, the cyclonic and the widely ?distorted? behavior of the surface extended interacting active regions, the occurrence of Coronal Holes (CH) unpredictable by dynamo classical models, the polar regions cycles and/or recurrences, the large dispersion of heights of SN cycles etc. are however the subject of hot debates. More important for practical obvious reasons is the prediction of the solar cycles in advance. The solar activity through the sunspot cycles (SN) modulates géomagnetism, CMEs, flares, SEPs and associated disturbances. It has been naively suggested (following the Ohl?s law) that the Polar Regions activity, with the occurrence of recurrent géo-activity in the years before and around the solar minimum of SN cycle n is rather correlated with the height of the n+1 cycle of SN. Accordingly the height of the following SN cycle could be predicted; additionally, there is now a growing consensus on the key role of polar magnetic fields as seeds for the SN cycles.

We looked at the activity of Polar Regions using proxies: i/ density of polar faculae from visually evaluated HMI of SDO mission W-L filtergrams; ii/ numbers of cool ejection events from a 15 Years survey of the Pic du Midi CLIMSO Ha observations; iii/ averaged extensions of the 304 shell in Polar Regions related to the polar CHs macro- spicules activity. Time variations of these parameters qualitatively point to a cycle 25 that could reach high levels, of order of 2 times the height of the cycle 24, in contrast with the moderate height predicted by the Solar Cycle 25 Prediction Panel of NASA and NOAA (Chair: Doug Biesacker). The reason of this discrepancy is not clear. We better wait the occurrence of the double maximum of SN of cycle 25 in 2025- 26. Another interesting parameter seemingly related to this topic is the definite observation of the chromospheric prolateness (ovalisation) in the Years of the minimum of 2018- 2020 that was discovered in the Years 1998- 2020 (before cycle 23) and that was not well measured in 2010- 11 (before cycle 24).

“Observation of the Initial Phase of CMEs through the Polarimetric W-L Coronagraphy”

by

Serge Koutchmy (1), Serge Rochain (2), François Sèvre (1), Jacques-Clair Noëns (2), Frederic Pitout (3), Claude Aime (4) and Boris Filippov (5)

(1) IAP- CNRS and Sorbonne Univ. (2) Association des O.A., Obs. Pic du Midi

(3) IRAP - Univ. Toulouse 3/ CNRS ; (4) Nice Univ. Sophia Antipolis/ CNRS, UMR7293 ,

(5) Pushkov IZMIRAN, Fedération Russia

Abstract: The next few decades will see the development of new facilities to support coronal mass ejection (CME) observations that are the critical part of the space weather. CMEs, radiations and particles from flares are particularly hazardous to many critical civilian space systems and to sensitive ground-based economic targets, especially during the sunspot activity. The important phase of the initiation process at the origin of CMEs in the low corona is still mysterious: eruptions of filaments and prominences, a rising hot coronal cavity, explosions induced by eruptions and waves coming from flaring regions with coronal enhancement above, X-EUV radiations of coronal magnetic loops, interactions of the large-scale arch systems with subsequent magnetic reconnections, magnetic clouds and plasmoids, etc. are suggested. Routine X-EUV space instruments will continue to provide instantaneous coronal images of multi-line emissions without direct measurements of coronal densities in the inner and intermediate corona. These parameters can be diagnosed using the Thomson electron scattering of the white light (WL) intensities coming from the visible disc. Proper motions of structures are visualized. Externally occulted spaceborne coronagraphs cannot access the internal coronal regions. Routine observations from ground-based sites, with the help of advanced Amateurs, are needed. The Lyot-type “K-coronameter” has been successfully used in the past at the Pic du Midi Observatory to study the brightest regions of the very inner corona. The full corona is today observed using modern technologies at the unique site of the MLSO (Hawaii) where synthetic pB images are made available. Thanks to the polarimetric CMOS camera recently placed on the market and the large coronal photon flux available in WL, it is proposed to use an externally occulted small aperture low budget coronagraph to carry out these observations. A first project is discussed within the framework of the Association "Observateurs Associés" of the Pic du Midi Observatory. This instrument could take advantage of the existing large equatorial mount used for the so-called "CLIMSO" coronagraphs which analyze the innermost corona with very narrow filters. Data on the electron corona, over a radial field of view of 3 solar radii, can be collected by recording polarized images in WL (pB) to make movies, etc. provided a fast digital processing is done to remove the unpolarized background. The instrumental parameters of this original coronagraph and the first results of laboratory measurements using an artificial Sun will be illustrated. The calibration plans to be performed during total solar eclipses and also outside, using simultaneously recorded bright stars, will be briefly mentioned.

References:

- “Fresnel diffraction of multiple disks on axis- Application to coronagraphy” , Cl. Aime (2020) , Astron.

Astrophys. 637, A16

- « Polarimetric Studies of a Fast Coronal Mass Ejection », Mierla, M. Inhester, B. Zhukov, A. Shestov, S.

Bemporad, A. Lamy, Ph. and Koutchmy, S. (2021) Solar Physics, submitted.

- « Real-time image processing and data handling for ground-based and spaceborne coronal

observations », Koutchmy, S. Colley, S ; Smartt, R. Nitschelm, C. and Zimmerman, J-P. . , (1990), Proc. SPIE

1235, Instrumentation in Astronomy VII, (1 July 1990); doi: 10.1117/12.19149

- “Improved Measurements of the Scattered Light Level Behind Occulting Systems”, Koutchmy, S.

Belmahdi, M. (1987), J . Optics (Paris)., vol. 18, nos 5-6, pp. 265-269

- “Measuring Electron Density in coronal active regions”, Noëns J.C. and J-L. Leroy (1981), Solar Phys. 73,

81-87

Density inhomogeneities are ubiquitous in space and astrophysical plasmas, in particular at contact boundaries between different media. They often correspond to regions that exhibits strong dynamics on a wide range of spatial and temporal scales. Indeed, density inhomogeneities are a source of free energy that can drive various instabilities such as, for instance, the lower-hybrid-drift instability which in turn transfers energy to the particles through wave-particle interactions and eventually heats the plasma. The goal of our work is to quantify the efficiency of the lower-hybrid-drift instability to accelerate and/or heat electrons parallel to the ambient magnetic field. To reach this goal, we combine two complementary methods: full-kinetic and quasilinear models. We report self-consistent evidence of electron acceleration driven by the development of the lower-hybrid-drift instability using 3D-3V full-kinetic numerical simulations. The efficiency of the observed acceleration cannot be explained by standard quasilinear theory. For this reason, we develop an extended quasilinear model able to quantitatively predict the interaction between lower-hybrid fluctuations and electrons on long time scales, now in agreement with full-kinetic simulations results. Finally, we apply this new, extended quasilinear model to a specific inhomogeneous space plasma boundary: the magnetopause of Mercury, and we discuss our quantitative predictions of electron acceleration in support to future BepiColombo observations.

The electron density in the topside ionosphere recorded by the Langmuir probes on board the Swarm satellites have been systematically analyzed to determine the climatology of the Equatorial Ionization Anomaly (EIA). The annual variation of the electron density in low- and mid-latitude topside ionosphere at different local time sectors show slower electron densities during nighttime than daytime. During the day, the ionospheric density starts to increase at mid-latitudes, with a single crest between 8 LT and 12 LT. It is also noticeable that the double crest structure is clearly present between 12LT and midnight; symmetric from noon to 20 LT and asymmetric from 20 LT to 24 LT. Observations show strong seasonal variations, with the electron density being lower around the June solstice compared to the rest of the year. We have noticed the semi-annual anomaly:the electron density is higher around equinox than around solstice. For solstice seasons,the asymmetries in the electron density with respect to the magnetic equator are stronger at the December solstice than at the June solstice. For equinox seasons, we can notice equinoctial symmetry in all local time sectors, meaning that the same t rend is observed for both equinoxes with or without symmetrical crests.

SEPs are correlated with the 11-year solar cycle due to their production by flares and interaction with the inner heliosphere, while GCRs are anti-correlated with it due to the modulation of the heliospheric magnetic field. The solar magnetic field along the cycle varies in amplitude but also in geometry, causing diffusion of the particles along and across the field lines; the solar wind distribution also evolves, and its turbulence affects particle trajectories.

We combine 3D MHD compressible numerical simulations to compute the configuration of the magnetic field and the associated polytropic solar wind up to 1 AU, with analytical prescriptions of the corresponding parallel and perpendicular diffusion coefficients for SEPs and GCRs. First, we analyze separately the impact of the magnetic field amplitude and geometry for a 100 MeV proton. By varying the amplitude, we change the amplitude of the diffusion by the same factor, and the radial gradients by changing the spread of the current sheet. By varying the geometry, we change the latitudinal gradients of diffusion by changing the position of the current sheets. We also vary the energy, and show that the statistical distribution of parallel diffusion is different for SEPs and GCRs. Then, we use realistic solar configurations, showing that diffusion is highly non-axisymmetric due to the configuration of the current sheets, and that the distribution varies a lot with the distance to the Sun, especially at minimum of activity. With this model, we are thus able to study the direct influence of the Sun on Earth spatial environment in terms of energetic particles.

R. F. Pinto¹, Q. Noraz¹, A. S. Brun¹, V. Archontis², A. Borissov²

¹ Département d’Astrophysique/AIM, CEA/IRFU, CNRS/INSU, Univ. Paris-Saclay & Univ. de Paris, 91191 Gif-sur-Yvette, France
² School of Mathematics and Statistics, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK

Twisted magnetic flux-ropes play an extremely important role on the dynamics of the surface of the Sun and of the corona across a wide range of scales. They contribute to the formation of active regions, to the triggering of flares and CME, and to the renewal of the large-scale coronal magnetic field during the solar cycle. Such flux-ropes are generated deep inside the Sun's convection zone. Under the right circumstances, they -- or at least some portions of them -- will rise buoyantly across the turbulent convective layers and emerge.
We report on the development of new three-dimensional MHD numerical simulations that extend from the deep inner Sun to the the solar atmosphere using the ASH code (internal Sun) coupled to the LaRe3D code (near photospheric layers to low corona). Our numerical setup describes the dynamical evolution of buoyant Omega loops that form from twisted flux-ropes at the bottom of the convection zone until their post-emergence phases. We aim at relating the properties of the flux-emergence events to those of their precursors and to the dynamical properties of the turbulent convection zone.
This project in run under the ERC Synergy project WholeSun.

There are many reasons that may explain why the two Earth’s magnetospheric cusps display interhemispheric asymmetries in their location, dynamics, or properties. Among these reasons are the tilt angle of the magnetic axis, the difference in insolation of the two ionospheres, and asymmetries in the solar wind penetration processes. In this study, we present an event of simultaneous observations of the northern and southern mid-altitude polar cusps by the Polar spacecraft and Cluster fleet that may shed light of this matter. We examine the possible asymmetries in the fields and plasma parameters, although the proximity of the equinox should limit these asymmetries. Ion sensors reveal two dispersions in both cusps and data analysis leads to the conclusion that those dispersions are due to pulsed reconnection at a single X-line, which runs along the subsolar magnetopause. While the electromagnetic and particle energy fluxes injected in both cusp are globally very similar, we report significant differences in ion dispersions, width of the low-latitude boundary layer and peak convection velocities. We ascribe these differences to the dipole tilt that is large enough to introduce an asymmetry in the magnetosheath flow at the exterior cusps.

The New Astrometric Reduction of Old Observations NAROO center is built at Paris Observatory, Meudon, and is dedicated to the measurement of astro-photographic plates and the analysis of old observations. The NAROO digitizer consists of a granite based Newport-Microcontrol open frame air-bearing XY positioning table, a scientific sCMOS camera, and a telecentric optical system. The plate holder assembly is suited for mounting glass plates up to 350-mm square. The machine positioning stability is better than 15 nm, its repeatability is better than 40 nm. With real photographic plate data, we are able to produce measurements with an accuracy better than 65 nm.

The renewed interest about photographic plates concerns the expansion of the database of transient objects evolving in time, since digitization now makes it possible to measure images with a high level of accuracy and to identify all the available objects. The information extracted from such materials can be of an astrometric, photometric, and spectroscopic nature, when not purely imaging, with consequences in planetology, near-Earth asteroid risk assessment, astrophysical phenomena, and general relativity, to mention but a few. 

We will present first research possibilities for Solar photographic plates to be digitized and analyzed. We will also give details for the researchers to use our facilities and digitize their collection by answering our Call for Proposals.

Il est connu que la compréhension des comportements de l’ionosphère Terrestre durant les tempêtes géomagnétiques et surtout l’origine des orages positives (augmentation de densité électronique Ne par rapport au calme) et négatives (diminution de Ne par rapport au calme) représente une tâche importante à accomplir en météorologie de l’espace. Dans ce cadre nous avons comparés les données de densité électronique Ne et de densité des neutres Dn fournis par les trois satellites SWARM, durant trois tempêtes géomagnétiques intenses 17-18 mars, 22-23 juin, 7-8 octobre 2015 à celles des jours calmes dans le but de comprendre les origines des orages positives (+) et négatives (-) au niveau de la région ionosphérique F et surtout au-dessus de pic de plasma.

Au début de la phase principale de ces trois tempêtes l’ionosphère terrestre a marqué simultanément un orage(+) dans le coté jour et un orage(-) dans le côté nuit, où la composante Bz du champ magnétique interplanétaire (IMF) est dirigé vers le sud, et Ey du champ électrique interplanétaire (IEF) est dirigé vers le soir. Ce qui confirme que ces deux phénomènes qui ont affectés l’ionosphère au début de cette phase sont dus principalement au champ électrique à pénétration rapide (PPEF) dû aux fuites du champ électrique de convection vers les basses latitudes. Plus tard et lorsque Bz du (IMF) s’est dirigé vers le nord, l’orage(+) a persisté dans le coté jour et est apparu aussi dans le coté nuit (sauf pour la tempête d’octobre où le coté nuit a été marqué par un orage (-) durant toute cette tempête) avant qu’il devienne (-). Durant cette étape la densité des neutres Dn a marqué une augmentation des pôles vers l’équateur qui est plus important dans l’hémisphère nord que dans l’hémisphère sud. Ce nous fait suggérer que l’orage (+) tardif est probablement due à deux autres mécanismes que le PPEF, qui sont le champ électrique dynamo de perturbation (DDEF) et les perturbations de la circulation thermosphérique générée par le chauffage joule causé par la pénétration des particules de haute énergie des vents solaires vers les zones polaires pendant les tempêtes géomagnétiques. Tandis que le couplage thermosphère/ionosphère conduit à un écoulement de plasma vers les zones où les taux de perte sont élevés ce qui signifier que les orages (-) sont plus probablement attribués au changement des compositions neutres.

Mots-clés : Mission SWARM, Tempête géomagnétique, Ionosphère supérieur, densité d'électrons, densité des neutres, champ électrique à pénétration rapide PPEF, champ électrique dynamo de perturbation DDEF.